An experimental and theoretical study of the critical fusion frequency as a function of stimulus duty ratio

Many researches in recent years have focused on the importance of the time domain in the visual system. For instance, the critical fusion frequency (CFF) has been extensively used to evaluate the visual temporal processing. Not only has CFF been proposed as a diagnostic tool for certain nervous system disorders, but it has also been used to quantify cognitive side effects in workplace fatigue. Thus a detailed knowledge of CFF will help to develop several applications. CFF depends on a number of factors, for example, it is known to increase with log-luminance (Ferry-Porter law). In this research, we focused on duty-ratio dependence because the duty ratios of the driving pulses used in previous studies were only 50% or due to several duty ratios. Specifically, we measured CFF values as a function of the duty ratio of the light source in more detail than in previous studies. We used a simple CFF measurement system based on a microprocessor (Raspberri-Pi) controlled by a Python code, that is, an analog signal output device was used to drive a single LED, control the flickering frequencies, switch the flickering duty ratios and record the perceived CFF threshold. As a result, we found a sharp decrease in CFF when the duty ratio reached 80% (light-time) or higher. Furthermore, we made a theoretical model based on biological known eye parameters. We calculated the contrast from signals perceived on the retina and simulated CFF with a certain threshold value. These signals on the retina were derived using the convolution of the stimuli with the temporal impulse response of the visual system. Overall, the simulated CFF theoretical model match our data within our experimental error bar (about 10%) indicating that our model can explain CFF in a rigorous quantitative framework.